A. Field of the Invention
The present invention relates to a variable camber airfoil, and more particularly to an apparatus particularly adapted to vary the camber of the leading edge portion of an airfoil.
B. Brief Description of the Prior Art
A common way of modifying the lift characteristics of an airfoil for low speed operation is to use leading edge devices which either pivot or slide outwardly from the leading edge of the airfoil to a deployed position. With many such devices, there is the problem that during deployment there is an interruption of smooth airflow over the airfoil. Also many of these devices are not able to be deployed to intermediate positions while maintaining the proper flow of air over the airfoil.
Accordingly, there have appeared in the prior art various devices to vary the shape of the airfoil itself in a manner to change the camber and thus modify its lift characteristics. One such device is shown in U.S. Pat. No. 1,763,888, Griswold II, in which the nose section of an airfoil is pivotally mounted at its upper rear end to the aircraft structure. A bell crank is attached to the lower portion of the nose to deflect it downwardly for increased camber. A somewhat similar device is shown in U.S. Pat. No. 2,650,047, Carhart et al, where the nose section of the airfoil is pivotally mounted to an intermediate link which is in turn mounted to the airfoil frame so that the nose can be deflected downwardly to increase the camber of the airfoil.
Another device to deflect the nose end of an airfoil downwardly is shown in Brady et al, U.S. Pat. No. 2,749,060, where the nose section is mounted to the main frame of the airfoil by means of two pivotally mounted links. The two links are so positioned that as the lower link is pulled rearwardly, the nose of the airfoil follows a path which resembles downward pivotal movement about a point at the forward end of the airframe.
U.S. Pat. No. 1,828,981, Parker, shows a mechanism to modify the camber along the entire chord length of the airfoil. This is accomplished by connecting the lower skin of the airfoil to a plurality of pivotally mounted links, the angular positions of which are offset with respect to one another. Rotation of these links causes the middle portion of the lower skin to deflect upwardly, while the trailing edge portion of the airfoil is deflected downwardly. U.S. Pat. No. 2,022,806, Grant, shows another mechanism for changing the camber along substantially the entire chord length of the wing by providing the wing with a supporting framework made up of a plurality of triangular trusses, the lower ends of which can be moved relative to each other. By moving the lower ends of the trusses either closer or further away from one another, the length of the lower skin of the wing can be changed with respect to the length of the upper skin, so as to cause a corresponding change in the camber of the wing.
In U.S. Pat. No. 2,763,448, Davie Jr., a roller is positioned inside the leading edge of the airfoil, and the location of this roller is modified by a cable mechanism to change the configuration of the leading edge of the airfoil.
In U.S. Pat. No. 3,836,099, O'Neill et al, there is shown a mechanism to vary the camber of the leading edge of an airfoil in a manner that the upper forward skin section of the airfoil is bent in a more or less continuous curve from the nose section back to the main airfoil section. In this mechanism, the upper and lower forward skin sections are interconnected by a plurality of diagonal links, the lower ends of which are interconnected by a plurality of bell cranks operated from a common actuating arm. By moving the actuator arm rearwardly, the several bell cranks cause the forward lower skin section to contract, and thus deflect the nose downwardly and rearwardly.
U.S. Pat. No. 3,941,334, Cole, shows several different mechanisms for deflecting both the leading and trailing edges of an airfoil. In general, these devices comprise a rib beam or the like which extends into the cambered section, with this rib beam being deflected upwardly or downwardly to change the camber. The rib beam has associated linkage to deflect the extreme outer portion of the cambered section to an angle greater than the deflection of the rib beam itself.
While the prior art has provided devices which are operable to change the camber of an airfoil, there is still a continuing need to seek improvements with regard to simplicity and reliability of structure and operation, and also to accomplish the change of camber so that the airfoil, particularly with regard to the upper surface, is always in a smooth continuous curve with no significant surface discontinuities to induce flow separation.